The present invention relates to a rotating clutch assembly for an automatic transmission in which no return spring is needed as a result of an enlarged compensator cavity.
Clutch assemblies are used in automatic transmissions to selectively engage and disengage rotating members of different planetary gear sets. For example, a clutch may be engaged to connect the sun gear of a first planetary gear set to a ring gear of a second planetary gear set. The clutch typically includes a hydraulically-actuated piston and a series of clutch plates.
A typical prior art rotating clutch system 10 is shown in FIG. 1. As shown, the rotating clutch system 10 selectively connects a first rotatable member 12 with a second rotatable member 14 by engagement of the clutch pack 16. The various components shown in FIG. 1 are arranged concentrically about the centerline 18 of the transmission.
The rotating clutch system 10 includes a compensator 20 and a movable piston 22. A clutch housing 24 encloses the piston 22, compensator 20, and clutch pack 16.
A piston cavity 26 is formed between the housing 24 and the piston 22 to receive fluid from a clutch apply feed orifice 28. A compensator cavity 30 is formed between the compensator 20 and the piston 22 to receive fluid from a compensator feed orifice 32.
The piston 22 includes an abutment end 34 which selectively engages the clutch plate 36 when the piston 22 is applied to compress the clutch pack 16 to engage the first and second rotatable members 12, 14.
A return spring 38 is provided in the compensator cavity 30 between the compensator 20 and piston 22 to bias the piston 22 away from the clutch pack 16 to assure that the piston 22 is in a disengaged position with respect to the clutch pack 16 when the clutch housing 24 is rotating and the piston clutch is desired released, and to assist the fluid in the compensator cavity 30 in overcoming centrifugal pressure force which is applied against the piston 22 by fluid in the piston cavity 36.
It is desirable to improve upon prior art rotating clutch systems by reducing costs, improving packaging efficiency, reducing weight, easing assembly, and improving performance. Of course, the return spring 38 has a cost associated with the component, requires additional packaging space, adds mass to the assembly, and adds a step to the assembly process. A special tool is required to compress the spring to allow insertion of the compensator 20 so that the snap ring 40 may be installed.
Also, there may be a significant variation in the spring rate of the return spring as a result of manufacturing variations. The pressure required to stroke the piston against the spring may vary considerably as a result of such spring manufacturing variations, especially in light of the additional stack up tolerance of the clutch pack arrangement, which narrows the acceptable spring rate of the return spring. These matters complicate and add cost to the manufacturing and assembly processes associated with the clutch assembly. The performance of the transmission also benefits from the reduced variation in stroked return spring pressure by having more consistent shift-to-shift and transmission-to-transmission variation.
The present invention improves upon prior art rotating clutch systems by eliminating the return spring. This is achieved by enlarging the compensator cavity so that centrifugal pressure force against the piston from the compensator cavity is greater than the centrifugal pressure force against the piston from fluid in the piston cavity. In this manner, the return spring is eliminated.
More specifically, the invention provides a clutch assembly for a transmission which is configured to selectively interconnect a first rotatable member with a second rotatable member by engagement of a clutch pack. The clutch assembly includes a compensator and a piston which is axially movable with respect to the compensator and configured to selectively abut and engage the clutch pack to interconnect the first and second rotatable members. A clutch housing encloses the piston, compensator and clutch pack. The piston cavity is formed between the housing and the piston to receive fluid from a clutch apply feed orifice to actuate the piston. The piston cavity has an outer radius (Rop). A compensator cavity is formed between the compensator and piston to receive the fluid from a compensator feed orifice. The compensator cavity has an outer radius (Roc) which is greater than the outer radius (Rop) of the piston cavity. The ensures that the fluid in the compensator cavity acting on the piston provides a greater centrifugal pressure force than fluid in the piston cavity acting on the piston, thus allowing the piston to remain in a released state when the released state is desired. This eliminates the need for a return spring in the compensator cavity.
Preferably, the housing is integral with the first rotatable member. A snap ring is positioned to prevent axial movement of the compensator.
The piston is configured to form first and second cup-shaped portions. The first and second cup-shaped portions cooperate to form first and second steps in a radially outward direction. The housing is configured to form third and fourth cup-shaped portions aligned with the first and second cup-shaped portions of the piston, such that a rim of the housing between the third and fourth cup-shaped portions extends between the first and second steps, thereby reducing size of the housing to improve packaging efficiency.
In accordance with another aspect of the invention, a clutch assembly is provided for a transmission to selectively interconnect a first rotatable member with a second rotatable member by engagement of a clutch pack. The clutch assembly includes a compensator and a piston which is axially movable with respect to the compensator and configured to selectively abut and engage the clutch pack to interconnect the first and second rotatable members. A clutch housing encloses the piston, compensator and clutch pack. A piston cavity is formed between the housing and piston to receive fluid from a clutch apply feed orifice to actuate the piston. A compensator cavity is formed between the compensator and piston to receive fluid from a compensator feed orifice. The piston cavity and compensator cavity are configured such that fluid in the compensator cavity provides a greater centrifugal pressure force against the piston in a clutch release direction than fluid in the piston cavity provides against the piston in a clutch apply direction during rotation, thereby eliminating the need for a return spring in the compensator cavity.